Systems, methods, and computer programs for generating a measure of authenticity of an object

ABSTRACT

An imaging system ( 200 ) for generating a measure of authenticity of an object ( 10 ) comprises a dispersive imaging arrangement ( 30 ) and an image sensor arrangement ( 60 ). They are positioned so that, when electromagnetic radiation ( 20 ) from the object ( 10 ) illuminates the dispersive imaging arrangement ( 30 ), the electromagnetic radiation is dispersed and imaged by the image sensor arrangement ( 60 ). The imaging system ( 200 ) is configured to then generate a measure of authenticity of the object ( 10 ) depending at least on a relation between the imaged dispersed electromagnetic radiation and reference spectral information. The invention also relates to imaging methods, computer programs, computer program products, and storage mediums.

TECHNICAL FIELD

The present invention relates to systems for generating a measure ofauthenticity of an object. The invention also relates to methods,computer programs, computer program products, and storage mediums forthe same purposes.

BACKGROUND

The supply of counterfeit goods in a particular market causes a loss ofrevenue to manufacturers of the corresponding genuine goods, as well asto governments when those goods are subject to taxation. End users areadversely affected by counterfeit goods because they are supplied withproducts of inferior quality, which may even be dangerous to the healthof the end user for certain products, such as when medicines are thesubject of counterfeiting. The manufacturer of high-quality genuineproducts will consequently suffer a loss to its goodwill.

A number of anti-counterfeiting measures have been proposed in the priorart with respect, for example, to alcoholic and non-alcoholic drinks(beer, wine, liquor, soft-drinks, etc.), tobacco products (cigarettes,cigars, loose tobacco, etc.), medicinal products, perfumes and excisableproducts generally. It is known to make use of sophisticated printingtechniques to make the design on the package as hard to replicate aspossible.

It is also known to make use of fluorescing items that look one wayunder ambient light and look a different way under ultraviolet (UV)radiation. Also used are holographic images of varying degrees ofcomplexity. Other known techniques include watermark technology,engraved gravure lines and marks that change colour depending on heatapplied to the mark.

CN 202533362 U relates to a printed matter authenticity identificationdevice based on a multispectral imaging technology. The device comprisesa multispectral imager for carrying out multispectral scanning on a testsample (the multispectral imager comprising a light source, a grating,and an imaging detector), a spectral data processor for comparingspectral data obtained from scanning with spectral data of a standardsample, and a data server used for storing the spectral data of thestandard sample. If the difference between the spectral data obtainedfrom scanning and the spectral data of a standard sample exceeds a setthreshold value, the test sample is judged as fake. Otherwise, it isjudged as authentic.

The prior art also includes various imaging spectrometers used forscientific observations. These systems typically aim at obtaininghigh-resolution spatial and spectral information about all regions of ascene or object. In particular, imaging spectrometers are imagers thatallow extraction of three-dimensional spectral irradiance map of aplanar object (spatial-spectral data cube) I(x, y, Δ) by use oftwo-dimensional array detectors such as CCD (i.e., charge-coupleddevice) or CMOS (i.e., complementary metal-oxide-semiconductor) sensors.One dimension is the wavelength and the other two comprise the spatialinformation.

Two major categories of spectral imagers exist: the spectral scanningimagers and the snapshot spectral imagers. A review of multi- andhyperspectral imager can be found for example in Hagen et al, “Snapshotadvantage: a review of the light collection improvement for parallelhigh-dimensional measurement systems”, Optical Engineering 51(11),111702 (2012), and Hagen et al, “Review of snapshot spectral imagingtechnologies”, Optical Engineering 52(9), 090901 (September 2013).

One way to acquire three-dimensional information by a two-dimensionalsensor is to acquire sequentially images through mechanically scannedwheel or array of optical filters installed in front of an imager.Another possibility is to tune the central transmission band of a filtersuch as a multi-stage liquid crystal filter, an acousto-optic filter, ora Fabry-Perot interferometer. These two examples fall into the categoryof spectral scanning imagers.

Snapshot spectral imagers capable of simultaneous acquisition of imagesin different spectral bands through an array of filters exist and anexample is the multi-aperture filtered camera (MAFC), using lensletarrays with focal plane detector.

Transmission diffraction gratings based snapshot spectral imagingsystems also exist. An example is the computed tomography imagingspectrometer (CTIS) which either uses several crossed transmissiongratings or specifically designed Kinoform grating able to disperseseveral spectral orders around a zero order.

Computed tomography algorithms have to be used to reconstruct thespectral radiance of the object.

Another example with transmission diffraction grating is the codedaperture snapshot spectral imager (CASSI) which uses complex masks toshadow some parts of the image of the object in order to facilitate thespectra extraction.

Integral field imaging spectrometers rely also on diffraction gratingsto disperse the light. In these setups, the image is sliced by differentmethods to fit onto an input slit of a conventional spectrometer toextract spectra. Image slicing can be obtained either by use of fiberbundle and distributing individual fibers into an entrance slit, or byaperture division using lenslet array.

Fourier transform imaging spectrometers also exist in a separatecategory. An interferometer is scanned to obtain images at differentoptical path differences and spectra are reconstructed by Fouriertransform. Some setups rely on lenslet array to do aperture division andanalyse the average spectra at different parts of the image/object. Anexample is the multiple-image Fourier transform spectrometer (MIFTS)based on a Michelson interferometer. Another distinct example is thesnapshot hyperspectral imaging Fourier transform spectrometer (SHIFT)which uses pair of birefringent prisms to obtain different optical pathlengths.

In view of the above, there is a need for providing fast, simple,inexpensive, compact, and robust equipment for authentication purposes,in particular, but not only, for incorporation into hand-held auditdevices.

SUMMARY

To meet or at least partially meet the above-mentioned goals, systems,methods, computer programs, computer program products, and storagemediums according to the invention are defined in the independentclaims. Particular embodiments are defined in the dependent claims.

In one embodiment, an imaging system is provided for generating ameasure of authenticity of an object. The imaging system comprises oneor more image sensors, the one or more image sensors being hereinafterreferred to as “image sensor arrangement”, and one or more opticalelements, the one or more optical elements being hereinafter referred toas “dispersive imaging arrangement”. The dispersive imaging arrangementis so that, when electromagnetic radiation from the object illuminatesthe dispersive imaging arrangement, at least part of the electromagneticradiation is dispersed. Furthermore, the dispersive imaging arrangementis positioned relative to the image sensor arrangement in such a manneras to allow the image sensor arrangement to image said dispersedelectromagnetic radiation. The imaging system is configured for, afterthe image sensor arrangement has imaged the dispersed electromagneticradiation in at least one imaging period, generating a measure ofauthenticity of the object depending at least on a relation between theimaged dispersed electromagnetic radiation and reference spectralinformation.

Such an imaging system enables the efficient verification of whether,and/or the extent to which, the relation between the imaged dispersedelectromagnetic radiation and reference spectral information, whichrepresents the expected spectral composition of the electromagneticradiation from the object, matches the predicted physics, in a situationin which some information about the electromagnetic radiation prior todispersion, i.e. some spatial information about the source of theradiation, is known or assumed (such as for example spatial informationabout the type of mark, sign or code that the imaged object bears). Ifthe relation matches the predicted physics, the object is likely to beauthentic. Otherwise, the object is more likely to be a counterfeit.

The invention also relates, in one embodiment, to an imaging method forgenerating a measure of authenticity of an object. The imaging methodmakes use of: one or more image sensors, the one or more image sensorsbeing referred to, as mentioned above, as “image sensor arrangement”,and one or more optical elements, the one or more optical elements beingreferred to, as mentioned above, as “dispersive imaging arrangement”.The dispersive imaging arrangement is so that, when electromagneticradiation from the object illuminates the dispersive imagingarrangement, at least part of the electromagnetic radiation isdispersed. Furthermore, the dispersive imaging arrangement is positionedrelative to the image sensor arrangement in such a manner as to allowthe image sensor arrangement to image said dispersed electromagneticradiation. The imaging method comprises: imaging, by the image sensorarrangement, the dispersed electromagnetic radiation in at least oneimaging period, and generating a measure of authenticity of the objectdepending at least on a relation between the imaged dispersedelectromagnetic radiation and reference spectral information.

The invention also relates, in some embodiments, to a computer programor a set of computer programs for carrying out an imaging method asdescribed above, to a computer program product or a set of computerprogram products for storing a computer program or a set of computerprograms as described above, and to a storage medium for storing acomputer program or a set of computer programs as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention shall now be described, inconjunction with the appended figures, in which:

FIG. 1 schematically illustrates an object to be imaged and an imagingsystem in one embodiment of the invention;

FIG. 2 schematically illustrates an object to be imaged and a system inone embodiment of the invention, wherein the system comprises both animaging system and an illumination arrangement;

FIG. 3 schematically illustrates an object to be imaged and a system inone embodiment of the invention, wherein the system notably comprisesillumination elements arranged around a dispersive imaging arrangement;

FIGS. 4 to 6 schematically illustrate three imaging systems and objectsto be imaged, in three embodiments of the invention respectively;

FIGS. 7 and 8 schematically represent, using a thin lens-gratingapproximation, two imaging systems and marks to be imaged, in twoembodiments of the invention respectively;

FIG. 9a schematically illustrates an imaging system in one embodiment ofthe invention, wherein the imaging system is an imaging device;

FIG. 9b schematically illustrates a system in one embodiment of theinvention, wherein the system comprises both an imaging system and anillumination arrangement, and wherein the system is an imaging device;

FIG. 10a schematically illustrates an imaging system in one embodimentof the invention, wherein the imaging system comprises an imaging deviceand said imaging device comprises an image sensor arrangement and adispersive imaging arrangement, but said imaging device is notconfigured to actually generate the measure of authenticity;

FIG. 10b schematically illustrates a system in one embodiment of theinvention, wherein the system comprises an imaging device and saidimaging device comprises an image sensor arrangement, a dispersiveimaging arrangement and an illumination arrangement, but said imagingdevice is not configured to actually generate the measure ofauthenticity;

FIG. 11 is a flowchart of an imaging method in one embodiment of theinvention;

FIG. 12 is a flowchart of an imaging method in one embodiment of theinvention, wherein generating the measure of authenticity comprisesdeconvolving the dispersed electromagnetic radiation by referencespectral information;

FIG. 13 is a flowchart of an imaging method in one embodiment of theinvention, including an assessment as to whether a deconvolution resultis decodable;

FIG. 14 schematically illustrates the processing of imaged dispersedelectromagnetic radiation for the purpose of authentication, in oneembodiment of the invention, wherein the object bears a two-dimensionalmatrix barcode;

FIG. 15 schematically illustrates the processing of imaged dispersedelectromagnetic radiation for the purpose of authentication, in oneembodiment of the invention, wherein the object bears a printed pattern(being a star-shaped logo);

FIG. 16 schematically illustrates the processing of different imageddispersed electromagnetic radiation for the purpose of authentication,in one embodiment of the invention;

FIG. 17 shows computed authentication parameters, or measures ofauthentication, corresponding to the five spectrum profiles of FIG. 16,in one embodiment of the invention;

FIGS. 18 to 21 provide further explanations regarding some embodimentsof the invention;

FIG. 22a schematically illustrates an imaging system in one embodimentof the invention, when applied, by simulation, to a single dot of atwo-dimensional matrix barcode;

FIG. 22b schematically illustrates an imaging system in one embodimentof the invention, when applied, by simulation, to a two-dimensionalmatrix barcode;

FIGS. 23 and 24 schematically illustrate two imaging systems in twoembodiments of the invention, respectively;

FIGS. 25 and 26 schematically illustrate the generation of a measure ofauthenticity of an object, in two embodiments of the invention, whereinthe image sensor arrangement images the dispersed electromagneticradiation in a plurality of illumination periods;

FIGS. 27 and 28 are flowcharts of imaging methods in two embodiments ofthe invention, wherein the generation of the measure of authenticity ofan object follows the image sensor arrangement imaging the dispersedelectromagnetic radiation in a plurality of illumination periods;

FIGS. 29a and 29b show images of a soft-drink can cap without (FIG. 29a) and with a mask (FIG. 29b ) acquired using an imaging system in oneembodiment of the invention;

FIG. 30 shows examples of images of a soft-drink can cap acquiredwithout a physical mask but excited in two different illuminationperiods by blue light (left-hand image) and green light (right-handimage), in one embodiment of the invention;

FIG. 31 shows examples of background-subtracted images using twodifferent linear combinations, in one embodiment of the invention;

FIG. 32 shows the spectral reflectivity of two different colourpigments;

FIG. 33 shows the typical relative spectral distribution of a white LED;

FIG. 34 shows the typical relative spectral distribution of anincandescence bulb at 3000 K temperature, compared to the one of thesun;

FIG. 35 shows the excitation spectrum and emission spectrum of anexemplary fluorescent dye;

FIGS. 36 and 37 show the emission and excitation spectra for exemplaryphosphorescent phosphor pigments;

FIG. 38 is a schematic diagram of an exemplary implementation of acomputing unit according to one embodiment of the invention;

FIG. 39 schematically illustrates an example of imaging period andillumination period, in one embodiment of the invention; and

FIG. 40 schematically illustrates an imaging system comprising, on theone hand, an imaging device comprising an image sensor arrangement,wherein the imaging device is a mobile phone having a camera, and, onthe other hand, an imaging accessory comprising a dispersive imagingarrangement.

DETAILED DESCRIPTION

The present invention shall now be described in conjunction withspecific embodiments. These specific embodiments serve to provide theskilled person with a better understanding, but are not intended torestrict the scope of the invention, which is defined by the appendedclaims. A list of abbreviations and their meaning is provided at the endof the detailed description.

FIG. 1 schematically illustrates an imaging system 200 in one embodimentof the invention. System 200 aims at generating a measure ofauthenticity of an object 10, i.e. an article. Object 10 may for examplebe, without being limited to, a bottle or can of beer, wine, liquor orsoft-drink, a pack, packet or box of cigarettes or cigars, a medicinepack, a bottle of perfume, or any other excisable goods, a banknote, avalue paper, an identity document, a card, ticket, label, banderol,security foil, security thread or the like. Object 10 has at least onepart, surface or side bearing a visible or invisible mark, logo, sign,image, or pattern, for example printed with a printing ink and/orcoating, either printed on a label apposed on object 10 or printeddirectly on object 10 (such as on a cap, capsule or the like of object10, wherein the cap or capsule may for example have a colouredbackground). The expected spectral response of said part, surface orside, and possibly the ink thereon (which may or may not have, forexample, photoluminescent properties), when subject to particularillumination conditions, is known and constitutes the reference spectralinformation. Some spatial information about the visible or invisiblemark, logo, sign, image, or pattern that object 10 bears is also knownor assumed to be known, as will be explained below.

System 200 comprises an arrangement 60, hereinafter referred to as“image sensor arrangement” 60, consisting in one or more image sensors.System 200 also comprises another arrangement 30, hereinafter referredto as “dispersive imaging arrangement” 30, consisting in one or moreoptical elements.

In one embodiment, image sensor arrangement 60 comprises one or morearray CCD or CMOS detectors to record the intensity distribution of theincident electromagnetic energy. Dispersive imaging arrangement 30 notonly disperses electromagnetic energy but may also gatherelectromagnetic energy from object 10 and focus the electromagneticenergy rays to produce a dispersed image of object 10 onto an imageplane where image sensor arrangement 60 is positioned. In oneembodiment, dispersive imaging arrangement 30 comprises, on the onehand, at least one of a diffractive element, a refractive element, oneor more lenses, and an objective, in order to produce a dispersed imageof object 10 onto the image plane where image sensor arrangement 60 ispositioned, and, on the other hand, a long pass filter (also called“long-wavelength pass filter”) in order to limit the spectral range usedfor authentication.

System 200 may also comprise optionally various auxiliary elements (notshown in FIG. 1) such as for example any one or any combination of: a) ahousing for containing, covering and/or protecting dispersive imagingarrangement 30 and image sensor arrangement 60; b) supporting elementsintegrally formed within the housing, or attached thereto, to maintaindispersive imaging arrangement 30 in a fixed or substantially fixedrelative position with respect to image sensor arrangement 60; c) aprotective cover or protective covering means to be used between object10 and dispersive imaging arrangement 30 to avoid parasitic illuminationfrom ambient light and/or sunlight (in this case, a controlledillumination source may be contained within this protective cover); d)additional optical filters (long-pass, bandpass, etc.), which may forexample be advantageous if imaging system 200 operates in luminescencemode, to cut out the irradiation source reflection; e) a controller orcontrolling means or units for controlling the operation of image sensorarrangement 60 and other elements; f) outputting and inputting means forproviding information to and receiving information from an operator,such as a display screen, a keyboard, push-buttons, control knobs, LEDindicator lights, etc. (in that respect, see also FIG. 38 and thecorresponding description); and g) a battery for powering variouselectronic parts of system 200.

Dispersive imaging arrangement 30 is constituted and positioned so that,when electromagnetic radiation 20 from object 10 illuminates dispersiveimaging arrangement 30 or in particular a specific part, surface, side,aperture or opening thereof, at least part of radiation 20 is dispersed.The word “dispersive” means here: that separates in its constituentwavelength components. Arrangement 30 may for example comprise: adiffractive element, a transmission diffraction grating (also knownsimply as “transmission grating”, or rarely as “transmissive diffractiongrating”), a blazed transmission diffraction grating, a volumeholographic grating, a grism (also called “grating prism”), a reflectivediffraction grating, a dispersive prism, or a combination of any ofthose. If arrangement 30 diffracts radiation 20, dispersedelectromagnetic radiation 50 may be referred to as a non-zerodiffraction order part, such as for example the negative or positivefirst diffraction order part of the radiation.

Here are some examples of transmission gratings that may be used in someembodiments of the invention:

-   -   Example 1: Especially for a transmission grating mounted in        front of an objective (see also in that respect FIGS. 4 and 23),        a Thorlabs #GT13-06V (from Thorlabs, Inc., based in Newton,        N.J., U.S.) with grooves density 600 lines per mm (l/mm), blaze        angle 28.7°, size 12.7×12.7×3 mm from Schott B270 glass, may be        used.    -   Example 2: Especially for a transmission grating mounted between        an objective and the image sensor(s) (see also in that respect        FIGS. 5, 6, and 24), a Richardson grating 340056TB07-775R (from        Newport Corporation, based in Rochester, N.Y., U.S.) with        grooves density of 360 l/mm, blaze angle 21°, and size        12.7×12.7×3 mm, may be used.    -   Example 3: Especially for a back-mounted grating for extended        field of view, a Thorlabs #GTU13-06 with grooves density 600        l/mm, blaze angle 22°, and size 12.7×12.7×2 mm from fused        silica, may be used.

Electromagnetic radiation 20 coming from object 10 and illuminatingdispersive imaging arrangement 30 may originate in part or in full fromthe reflection of electromagnetic radiation emitted by anelectromagnetic radiation source (not shown in FIG. 1). Radiation 20from object 10 and illuminating arrangement 30 may alternatively, oradditionally, originate in part or in full from some form ofphotoluminescence (i.e., fluorescence or phosphorescence) of a substanceof object 10 upon or after the illumination of object 10 byelectromagnetic radiation emitted by an electromagnetic radiationsource. In both cases (i.e., radiation by reflection or by some form ofphotoluminescence), the electromagnetic radiation source may, in oneembodiment, be integrated with, or attached to, a housing containingimaging system 200 (or part thereof). Said electromagnetic radiationsource may for example be a light source, an infrared radiating source,and/or an UV radiating source. In one embodiment, the electromagneticradiation source is an illumination source controlled by, or togetherwith, system 200.

Electromagnetic radiation 20 coming from object 10 usually containsradiation of more than one wavelength, especially when object 10 isauthentic. That is, radiation 20 is usually polychromatic in the broadsense of the term, i.e. not necessarily limited to visible colours.Radiation 20 may for example be in any wavelength range encompassedbetween 180 nm (UV radiation) and 2500 nm (infrared radiation), i.e. inthe visible light range and/or outside that range (for example in thenear-infrared (NIR) or short-wavelength infrared (SWIR) range). Theportion of radiation 20 reaching arrangement 30 that is actuallydispersed may depend on the characteristics of the optical element(s)forming arrangement 30. For example, long pass filter may be used toselect the spectral range to be analysed.

Furthermore, dispersive imaging arrangement 30 is positioned relative toimage sensor arrangement 60 in such a manner as to allow arrangement 60to image, in one imaging period, dispersed electromagnetic radiation 50.

An example of image sensor that may be used in some embodiments of theinvention is: a ⅓-Inch Wide-VGA CMOS Digital Image Sensor MT9V022 fromON Semiconductor, based in Phoenix, Ariz., U.S. That sensor has752-by-480 pixels with size 6 μm forming active imager size withdimensions of 4.51 mm×2.88 mm and diagonal of 5.35 mm.

An imaging period is here defined as being the period during whichdispersed electromagnetic radiation 50 is acquired (as illustrated byFIG. 39).

In one embodiment, the imaging period has a duration having a valueselected from the range of 5 to 1200 ms, and preferably selected fromthe range of 10 to 800 ms, such as for example 10, 20, 30, 50, 75, 100,150, 200, or 300 ms.

An illumination period (as illustrated by FIG. 39) is here defined asbeing a period during which illumination conditions are consideredsufficiently constant for the purpose of imaging dispersedelectromagnetic radiation 50, and generating a measure of authenticitybased thereof.

The portion of electromagnetic radiation 20 illuminating and passingthrough dispersive imaging arrangement 30 (therefore being at leastdispersed in one set of directions, and being optionally non-dispersedin another set of directions) that is then actually detected by imagesensor arrangement 60 depends on the characteristics of its imagesensor(s). The electromagnetic radiation detected by the image sensor(s)may for example be in any wavelength range encompassed between 180 nm(UV radiation) and 2500 nm (infrared radiation), i.e. in the visiblelight range and/or outside that range (for example in the near-infrared(NIR) or short-wavelength infrared (SWIR) range). In that example, thelower limit of 180 nm may be imposed by material constraints of bothdispersive imaging arrangement 30 and image sensor(s) 60, whereas theupper limit of 2500 nm may for example be imposed by the spectralresponse of indium gallium arsenide-based (GalnAs) infrared detectors.In one embodiment, the electromagnetic radiation detected by imagesensor(s) 60 is in the range of visible light. In one embodiment, theelectromagnetic radiation detected by image sensor(s) 60 is in thewavelength range of 180 nm to 2500 nm, more preferably in the range of400 nm to 1000 nm.

Yet furthermore, imaging system 200 is configured for, after imagesensor arrangement 60 has imaged dispersed electromagnetic radiation 50in at least one imaging period, generating a measure of authenticity ofobject 10 depending at least on a relation between the imaged dispersedelectromagnetic radiation and reference spectral information. System 200thus enables the verification of whether, and/or the extent to which,the relation between the imaged dispersed electromagnetic radiation andthe reference spectral information, which represents the expectedspectral composition of electromagnetic radiation 20 coming from object10, is in accordance with the expected underlying physics of the system,in a situation in which some information is known (or assumed to beknown) about object 10 and/or mark 11 from which electromagneticradiation 20 is coming (by reflection and/or emission). This means thatsome spatial information about electromagnetic radiation 20 prior todispersion is known or assumed, such as for example spatial informationabout the type, form, shape, dimension, or other properties of a mark,sign, code, or pattern that object 10 bears and from which radiation 20is coming. If the relation matches the expected underlying physics ofthe system, object 10 is likely to be authentic. Otherwise, it is morelikely to be a counterfeit. System 200 thus enables a form ofmaterial-based authentication, such as for example at least one of: a)material-based authentication of the ink used to create a mark 11printed on object 10, and b) material-based authentication of object 10itself especially if object 10 is luminescing with a specific emissionspectrum or has a specific reflection or absorption spectrum.

The nature of the relation that is looked at, i.e. the relation betweenthe imaged dispersed electromagnetic radiation, the reference spectralinformation, and the known or assumed spatial information about theelectromagnetic radiation before dispersion, i.e. information about mark11 on object 10 (this spatial information is not required to be imagedby image sensor arrangement 60, but, in some embodiments, may), may beunderstood in the following sense. If the reference spectral informationcorresponds, substantially corresponds, or plausibly corresponds to thespectral composition of electromagnetic radiation 20 coming from imagedobject 10, the imaged dispersed electromagnetic radiation typicallyresembles (non-linear effects may also need to be taken into account)the result of the convolution of the electromagnetic radiation beforedispersion (i.e. information about mark 11 on object 10) with thereference spectral information, in which case object 10 is likely to beauthentic. In contrast, if the reference spectral information does notcorrespond or does not plausibly correspond to the spectral compositionof radiation 20 coming from imaged object 10, the imaged dispersedelectromagnetic radiation typically noticeably differs from the resultof the convolution of the electromagnetic radiation before dispersion(i.e. information about mark 11 on object 10) with the referencespectral information, in which case object 10 is likely to be acounterfeit.

More generally, the nature of the relation that is looked at, i.e. therelation between the imaged dispersed electromagnetic radiation, thereference spectral information, and the known or assumed spatialinformation about the non-dispersed electromagnetic radiation (asmentioned above, this spatial information is not required to be imagedby image sensor arrangement 60, but, in some embodiments, may), may alsosignificantly differ from a mere convolution, considering the existenceof non-linear effects. The nature of the relation may be determined a)based on the underlying physics and geometry, b) empirically, and/or c)by simulation (for example, using raytracing methods of commerciallyavailable solutions, such as e.g. Zemax optical design program,available from Zemax, LLC, based in Redmond, Wash., U.S.).

The underlying physics and geometry may include (i) the properties ofdispersive imaging arrangement 30, image sensor arrangement 60, thetransmission medium in between, etc., and (ii) effects of stretch of theimage in the direction of the dispersion (y axis), which may becompensated for by mapping of the y axis of the image to a new y′ axisusing a non-linear function. The image may be stretched due to 1)non-linear dispersion of the grating, 2) projection distortions, and/or3) optics-specific field aberrations.

The non-linear effects may also, in one embodiment, be modelled as arelation between the dispersed image, the non-dispersed spatialinformation, and the reference spectrum in a form being as close tolinear translation-invariant (LTI) as possible. In such a case, thedetermination of the non-linear effects may be performed for example bya) acquiring several dispersed images of objects 10 with a knownreference spectrum, and b) fitting the non-linear parameters totransform the relation to LTI.

One way to determine the non-linear effects, and therefore the nature ofthe relation to be looked at, may be a mathematical analysis of theoptical system and determination of the correction that has to or shouldbe applied to make the system LTI. This may be done using opticalequations for example found in textbooks such as Yakov G. Sosking,“Field Guide to Diffractive Optics”, SPIE, 2011. This may also be donenumerically using optical software such as for example ZemaxOpticStudio™, available from Zemax, LLC.

In one embodiment, dispersive imaging arrangement 30 disperseselectromagnetic radiation 20 using, for example, a diffraction grating,and the imaged dispersed electromagnetic radiation is consequently theoutput of the diffraction grating imaged onto image sensor(s) 60. Thediffraction grating structure may, in one embodiment, be optimized sothat most radiation goes in the first order and the grating has almostno efficiency in the zero order. A synthetic non-dispersed image may bereconstructed using the imaged dispersed electromagnetic radiation andthe expected electromagnetic spectrum (the reference spectralinformation), for example by deconvolution or by a deconvolution-likeoperation. A deconvolution algorithm based on fast Fourier transform(FFT) may for example be used. The algorithm may for example use a setof columns from the image extracted along the dispersion direction,comprising intensity profiles from the imaged dispersed electromagneticradiation.

The reconstructed, synthetic non-dispersed image may then be assessed onits own and/or in view of the known or assumed spatial information aboutthe electromagnetic radiation before dispersion (i.e. information aboutmark 11 on object 10), for the purpose of authenticating object 10. Inone embodiment, generating the measure of authenticity further comprisesdetermining at least one of:

-   -   a) a measure of decodability of an imaged machine-readable code        in the result of the deconvolution or deconvolution-resembling        operation (to take into account non-linear effects, as explained        above);    -   b) a measure of sharpness of the result of the deconvolution or        deconvolution-resembling operation;    -   c) a measure of blurriness of the result of the deconvolution or        deconvolution-resembling operation;    -   d) a measure of the dimension of the result of the deconvolution        or deconvolution-resembling operation;    -   e) a measure of the area of the result of the deconvolution or        deconvolution-resembling operation;

f) a measure of the full width at half maximum of a cross-section of theresult of the deconvolution or deconvolution-resembling operation; and

g) a measure of the similarity of the result of the deconvolution ordeconvolution-resembling operation, to a reference pattern.

In one embodiment, generating a measure of authenticity of object 10comprises authenticating it, i.e. determining that it is likely to beauthentic or not. In one embodiment, generating a measure ofauthenticity of object 10 comprises generating an authenticity measure(or index) such as for example a real value between 0 and 1, wherein ‘0’may mean “fully sure that the object is not authentic” and ‘1’ may mean“fully sure that the object is authentic”.

In practice, the authentication index typically does not reach the value‘1’ for all authentic objects (and ‘0’ for all non-authentic ones).Hence, in one embodiment, a threshold between ‘0’ and ‘1’ is defined(for example a value comprised between 0.80 and 0.90, and in particular0.85) above which the object is considered as authentic, and below whichthe object is considered as non-authentic. This threshold may forexample be defined through measurements on a set of authentic andnon-authentic objects. These measurements typically produce a bi-modaldistribution of indexes (i.e., one part for the authentic objectsconcentrated towards the value ‘1’ and one part for the non-authenticones below, both separated by a gap). The robustness of the method isdirectly related to the extent to which the two parts (modes) of theindex distribution are distant from one another. The threshold may thenbe placed in between either close to the index distribution of theauthentic objects to minimize false positives or closer to thenon-authentic index distribution to minimize false negatives.

If object 10 is, for example, a container or package containing somegoods, the generated measure of authenticity may merely amount to ameasure of authenticity of the goods determined through a mark or signexisting on the container or package (assuming that the container orpackage has not been tampered with), not necessarily directly enablingto authenticate the goods as such.

Since the dispersed form 50 of the electromagnetic radiation may beimaged in one imaging period, and since the imaging enables thereconstruction of a synthetic non-dispersed form of electromagneticradiation based on reference spectral information, system 200 may beregarded as a form of snapshot imager in the sense that the scene is notscanned during the imaging process.

FIG. 2 schematically illustrates an object 10 to be imaged and a system220 in one embodiment of the invention. System 220 comprises both animaging system 200 (as described above with reference to FIG. 1) and anillumination arrangement 210. In one embodiment, system 220 forms asingle device, such as for example a handheld, code reading andauthentication device.

Illumination arrangement 210 generates electromagnetic radiation 21 forilluminating object 10. In one embodiment, radiation 21 has knownparameters (e.g., spectrum, power, homogeneity, etc.) to allowexcitation of e.g. luminescence emission spectra to allow disperseimaging of object 10 and/or mark 11 for authentication. As explainedabove with reference to FIG. 1, electromagnetic radiation 20 originatesfrom object 10, and/or mark 11, and reaches imaging system 200.

In one embodiment, system 220 is connected to driving electronics andsensor reading electronics, so that, for example, image data outputtedby imaging system 200 may be transferred to a processing unit for datatreatment.

FIG. 3 schematically illustrates an object 10 to be imaged and a system220 in one embodiment of the invention, as a possible implementation ofthe system illustrated on FIG. 2. System 220 notably comprisesillumination elements 22 arranged around dispersive imaging arrangement30. Although two illumination elements 22 are shown in FIG. 3, anynumber of illumination elements 22 may be provided, such as for examplethree, four or more. Furthermore, in one embodiment, illuminationelements 22 are arranged symmetrically around dispersive imagingarrangement 30. The symmetric arrangement of illumination elements 22around arrangement 30 is advantageous for homogeneous illumination ofthe target surface of object 10.

FIGS. 4 to 6 schematically illustrate three imaging systems 200 in threeembodiments of the invention, respectively, showing possible componentsof dispersive imaging arrangement 30, such as a transmission grating 31,an imaging lens 32, an optical long-pass filter 33, and an additionallens arrangement 34.

Arrangement 30 of FIG. 4 comprises an imaging lens 32, a transmissiongrating 31 mounted in front of lens 32, and an optical long-pass filter33 mounted behind lens 32. This enables to produce low opticalaberrations by using the broad field-of-view of the lens objective.

In arrangement 30 of FIG. 5, both transmission grating 31 and opticallong-pass filter 33 are mounted behind lens 32. This enables to cancelthe dependence on the object position along the optical axis.

In the embodiment of FIG. 6, optical long-pass filter 33 is mounted infront of lens 32, and transmission grating 31 is mounted behind lens 32.Furthermore, an additional lens arrangement 34 is also mounted behindlens 32. This configuration enables to efficiently separate thedispersed image from the non-dispersed image (if any) and avoiddependence on the object position along the optical axis.

FIGS. 7 and 8 schematically represent, using a thin lens-gratingapproximation, two imaging systems 200 and marks 11 in two embodimentsof the invention, respectively, to help understand the deflection of thefirst-order image relative to the optical axis and definition of minimumwavelength of a spectral range which is analysed to authenticate mark11.

In FIG. 7, dispersive imaging arrangement 30 includes a lens, atransmission grating and a long-wavelength pass filter, to create thedispersed image on the image plane 65 where the image sensor(s) arepositioned. Dispersed beams 50-1 are for the shortest wavelength λ₁ andcreate dispersed image 51 corresponding to wavelength λ₁.

Imaging system 200 receives electromagnetic energy 20 originating fromobject 10 to create a dispersed part, which is shifted compared to theoptical axis (along which non-dispersed beams may optionally propagate)and is blurred by the spectrum of electromagnetic energy 20 impingingarrangement 30. The minimum shift depends on the minimum wavelengthpresent in the spectrum emitted by object 10 or depends on the minimumwavelength transmitted through arrangement 30. The minimum shift mayalso depend on some grating and system parameters (e.g. grooves density,order, and incident angle) which parameters define the angulardispersion of the grating.

The three discrete dispersed images of mark 11 on FIG. 7 correspond todiscrete wavelengths λ₁, λ₂ and λ₃. These discrete wavelengths cantherefore be conveniently resolved since the corresponding images do notoverlap.

FIG. 8 shows the imaging of an area 12 of object 10, wherein area 12contains a printed mark 11, which may be in any position or orientation.If mark 10 is outside area 12, imaging system 200 should be repositionedso as to have mark 11 within area 12. Dispersed image 51 of area 12contains the image of mark 11.

Image 51 corresponds to the minimum wavelength λ_(min) that can betransmitted by the system and defined by a cut-on wavelength of a longpass filter of arrangement 30. Reference 62 shows the deflectionrelative to the optical axis in the image plane.

In one embodiment, illumination arrangement 210 (not illustrated on FIG.8) illuminates only the portion of object 10 corresponding to area 12.Illumination arrangement 210, together with an optional protective cover(as mentioned above), may be designed to prevent ambient light fromreaching area 12, thus providing better conditions for code reading andauthentication.

Although, in the above-discussed embodiments, the non-dispersed(zero-order) radiation is not used (or not necessarily used) forauthentication, it is in any event advantageous to avoid overlapping ofthe zero- and first-order when arrangement 30 does produce both zero-and first-order parts. Indeed, if the order separation is notsufficient, the dispersed images may be affected by part of anoverlapping zero-order image. To avoid such a situation, a mask may beused to reduce the size of the area 12 of object 10 that is beingimaged.

The embodiments that are not using the non-dispersed (zero-order)radiation for authentication are advantageous notably in that theoptical aberrations for the first order may be optimized withoutconsideration for any degradation of the aberrations in the zero order.In other words, only acceptable optical aberrations for the first orderare needed. In addition, the embodiments that are not using thenon-dispersed (zero-order) radiation for authentication are alsoadvantageous in that there is no requirement to acquire both zero- andfirst-order images, so that larger first-order image may be acquired ofan image sensor of a given size.

FIG. 9a schematically illustrates an imaging system 200 in oneembodiment of the invention, which differs from imaging system 200 ofFIG. 1 in that system 200 of FIG. 9a specifically consists in a singleimaging device. In addition to dispersive imaging arrangement 30 andimage sensor arrangement 60 described with reference to FIG. 1, system200 comprises a processing unit 70 configured for receiving datarepresenting the imaged dispersed electromagnetic radiation (as detectedby arrangement 60), generating the measure of authenticity as describedwith reference to FIG. 1, and outputting information 80 representing thegenerated measure of authenticity to any kind of user interface of theimaging device and/or to an output port for transmission to one or moreother external devices (not shown in FIG. 9a ).

In one embodiment, the imaging device making up imaging system 200 ofFIG. 9a is a hand-held device. Such an imaging device can therefore beregarded as a hand-held audit device capable of generating a measure ofauthenticity of an object, and providing the authenticity measure to,for example, the device's operator.

FIG. 9b schematically illustrates a system 220 in one embodiment of theinvention, wherein system 220 comprises both an imaging system 200 andan illumination arrangement 210, and wherein system 220 is an imagingdevice. In other words, the embodiment of FIG. 9b may be regarded acombination of the embodiments described with reference to FIGS. 9a and2. In one embodiment, the imaging device making up system 200 of FIG. 9bis a hand-held device.

FIG. 10a schematically illustrates an imaging system 200 in oneembodiment of the invention, which differs from imaging system 200 ofFIG. 1 in that system 200 of FIG. 10a is shown as specificallycomprising more than one device. Namely, in the example of FIG. 10a ,system 200 comprises two devices: on the one hand, an imaging device 100comprising dispersive imaging arrangement 30 and image sensorarrangement 60 described with reference to FIG. 1, and, on the otherhand, a processing device 110 comprising a processing unit 70.Processing device 110, rather than imaging device 100, generates themeasure of authenticity (as described with reference to FIG. 1). To doso, data 90 representing the imaged dispersed electromagnetic radiationis transmitted from imaging device 100 to processing device 110. Data 90may be transmitted on any suitable wired or wireless channel using anytransmission format (such as for example using Internet Protocol (IP)packets, optionally encrypted). Then, within processing device 110, themeasure of authenticity is generated by processing unit 70, andinformation 80 representing the generated measure of authenticity maythen be outputted to a user interface of processing device 110 and/or toan output port for transmission to one or more other external devices(not shown in FIG. 10a ).

FIG. 10b schematically illustrates a system 220 in one embodiment of theinvention, wherein system 220 comprises an imaging device 100 and saidimaging device 100 comprises an image sensor arrangement 30, adispersive imaging arrangement 60 and an illumination arrangement 210,but imaging device 100 is not configured to actually generate themeasure of authenticity. In other words, the embodiment of FIG. 10b maybe regarded a combination of the embodiments described with reference toFIGS. 10a and 2.

In one embodiment, imaging device 100 of any one of FIGS. 10a and 10b isa hand-held device.

In one embodiment, processing unit 70 of any one of FIGS. 9a, 9b, 10aand 10b forms part of a computing unit such as for example the oneillustrated with reference to FIG. 38 (which is discussed below). Insuch a case, processing unit 70 of FIG. 9a or 9 b and processing unit503 of FIG. 38 may actually be the same element. Likewise, in such acase, processing unit 70 of FIG. 10a or 10 b (within processing device110) and processing unit 503 of FIG. 38 may actually be the sameelement.

In some embodiments, the imaging device making up imaging system 200 ofFIG. 9a or 9 b, or imaging device 100 illustrated in FIG. 10a or 10 bcomprises a handle integrally formed with the housing, or attachedthereto, to enable an operator to hold the imaging device towards to theobject to be imaged and authenticated.

In one embodiment, the imaging device making up imaging system 200 ofFIG. 9a or making up system 220 of FIG. 9b , or imaging device 100illustrated in any one of FIGS. 10a and 10b further comprises a storageunit (not shown in any of FIGS. 9a , 9, 10 a, and 10 b) for storing, forexample, the reference spectral information which is known in advanceand used for generating the measure of authenticity. The referencespectral information may be stored in the form of a reference spectralprofile.

FIG. 11 is a flowchart of a method in one embodiment of the invention,which makes use of an image sensor arrangement 60 and a dispersiveimaging arrangement 30, as described above with reference to FIGS. 1 to10 b. The method comprises the steps of imaging s300, by arrangement 60,in at least one imaging period, dispersed electromagnetic radiation 50,and generating s400 a measure of authenticity of object 10 depending atleast on a relation between the imaged non-dispersed electromagneticradiation and reference spectral information. Step s400 is carried outthrough convolution or deconvolution operation(s) (as discussed belowwith reference to FIG. 12) or through convolution-like ordeconvolution-like operation(s) to take into account non-linear effectsas explained above.

If imaging step s300 consists in imaging dispersed electromagneticradiation 50 in a single illumination period, step s300 precedesgenerating step s400, usually without overlap. However, if step s300consists in imaging dispersed electromagnetic radiation 50 in aplurality of illumination periods (typically under differentillumination conditions), imaging step s300 and generating step s400 mayoverlap (not shown in FIG. 11). Namely, the process of generating s400the measure of authenticity may begin based on image data recordedduring one or more illumination periods while imaging step s300 is stillunder way.

In one embodiment, generating s400 the measure of authenticity dependsat least on the extent to which the result of the deconvolution of theimaged dispersed electromagnetic radiation by the reference spectralinformation meets or has certain properties or characteristics. In oneembodiment, this may be implemented as illustrated by the flowchart ofFIG. 12, with a step s410 of deconvolving the imaged dispersedelectromagnetic radiation by the reference spectral information, thusoutputting a reconstructed, synthetic non-dispersed image, and a steps420 of assessing the deconvolution result.

In one embodiment, as illustrated by the flowchart of FIG. 13, step s420of assessing the deconvolution result is implemented by determining s422a measure of decodability of a synthetically produced machine-readablecode in the result of the deconvolution. If the decoding attempt s422 issuccessful s424 (“yes”), then object 10 is determined s426 to be likelyauthentic. By contrast, if the decoding attempt s422 is not successfuls424 (“no”), then object 10 is determined s428 to be likely acounterfeit.

FIG. 14 schematically illustrates a method in one embodiment of theinvention, in which a decodability assessment is performed to generates400 a measure of authenticity of an object 10. Two identical codes areshown on the left-hand side, wherein the first code has been printedusing ink A (upper left) and the second code has been printed using inkB (lower left). Dispersed electromagnetic radiation 50 is then imageds300 by image sensor arrangement 60. The respective dispersed image isthen processed s410 by means of a deconvolution or adeconvolution-resembling operation (to account for non-linear effects)based on the reference spectral information representing the spectrum ofink A (“Ref Spectrum A”) to output a reconstructed, syntheticnon-dispersed image (which is respectively illustrated on the right-handside of FIG. 14). It can be observed that the reconstructed, syntheticnon-dispersed image on the upper right of FIG. 14, which has beengenerated based on the imaged dispersed form of the code printed usingink A and the reference spectral information representing the spectrumof ink A, is decodable. It can be observed that, by contrast, thereconstructed, synthetic non-dispersed image on the lower right of FIG.14, generated based on the imaged dispersed form of the code printedusing ink B and the reference spectral information representing thespectrum of ink A, is not decodable. The code is not decodable becausethe spectral information differs from the authentic one and hence thedeconvolution produces a distorted synthetic image of the code, whichquality is insufficient for successful decoding.

This decodability determination s420 may lead or amount to adetermination that the object having a non-decodable code (after theabove-described processing) is fake or likely to be fake, whereas theobject having a decodable code is authentic or likely to be authentic.

FIG. 15 schematically illustrates a method in one embodiment of theinvention, in which an assessment is also performed to generate s400 ameasure of authenticity of an object 10. Two identical patterns (i.e., afour-pointed star-shaped sign) are shown on the left-hand side, whereinthe first pattern has been printed using ink A (upper left) and thesecond pattern has been printed using ink B (lower left). Dispersedelectromagnetic radiation 50 is then imaged s300 by image sensorarrangement 60 (see images on the left-hand side of FIG. 15). Therespective dispersed image is then processed s410 by means of adeconvolution or a deconvolution-resembling operation based on thereference spectral information representing the spectrum of ink A (“RefSpectrum A”) to output a reconstructed, synthetic non-dispersed image(see images on the right-hand side of FIG. 15). It is then determinedthat the reconstructed, synthetic non-dispersed image on the upper rightof FIG. 15, which has been generated based on the imaged dispersed formof the pattern printed using ink A and the reference spectralinformation representing the spectrum of ink A, has a pattern which canbe recognized and has parameters representing a sufficient imagequality, for example in terms of sharpness or blurriness. It isdetermined that, by contrast, the reconstructed, synthetic non-dispersedimage on the lower right of FIG. 15, generated based on the imageddispersed form of the pattern printed using ink B and the referencespectral information representing the spectrum of ink A, has a patternwhich cannot be recognized or which can be recognized but has parametersrepresenting an insufficient image quality, for example in terms ofsharpness or blurriness.

This recognition and parameter-based quality determination may lead oramount to a determination that the object having the pattern printedwith ink B is fake or likely to be fake (determination after theabove-described processing: non-recognizable pattern, or recognizablepattern but having insufficient quality parameters), whereas the objecthaving the pattern printed with ink A is authentic or likely to beauthentic (determination after the above-described processing:recognizable pattern having sufficient quality parameters).

FIG. 16 schematically illustrates an exemplary implementation of amethod in one embodiment of the invention, in which, in particular,images of dispersed electromagnetic radiation from five objects printedwith different inks—with ink spectrum A to E respectively—are processedfor the purpose of authentication. Dispersed electromagnetic radiation50 associated with the five objects are imaged (images on the left-handside of FIG. 16). The respective dispersed image is then processed bymeans of a deconvolution or a deconvolution-resembling operation basedon the reference spectral information representing the spectrum of ink A(“Ref Spectrum A”) to output a reconstructed, synthetic non-dispersedimage (images on the right-hand side of FIG. 16). It is then determinedthat the reconstructed, synthetic non-dispersed image has a value d(computed authentication parameter or measure of authentication) whichis above or below a threshold, as shown in FIG. 17. To do so, theintensity profile of the central column of each of the reconstructed,synthetic non-dispersed images is used for generating the measure ofauthenticity. This determination may lead or amount to a determinationthat an object is fake or likely to be fake, or, rather, authentic orlikely to be authentic.

In one embodiment, hereinafter referred to as “embodiment E1” (notillustrated in the drawings), a DataMatrix code, or any kind of machinereadable code, is printed on object 10 using an ink having a referencespectrum (reflectance or luminescence). After imaging s300 the dispersedelectromagnetic radiation (hereinafter referred to as the “first orderimage”), a measure of authenticity is generated s400 by deconvolvings410 the first-order image by the expected genuine ink response(reference spectrum) and therefore computing (reconstructing) asynthetic zero-order image. An attempt is then made s422 to decode theresulting zero-order image. If it can be decoded, object 10 is regardedas genuine. If it cannot be decoded, object 10 is regarded asnon-genuine.

In one embodiment, decoding quality metrics returned by the decoder isused for generating the measure of authentication s420. Quality metrics(from ISO/IEC 15415 Barcode Print Quality Test Specification-2D Symbols,see p. 31ff in section 4.6.1.2 entitled “Parameters Measured and theirSignificance” of “GS1 DataMatrix Guideline, Overview and technicalintroduction to the use of GS1 DataMatrix”, Release 2.2.1, Ratified,July 2015, retrieved fromhttp://www.gsl.org/docs/barcodes/GS1_DataMatrixGuideline.pdf) may forexample be at least one of:

-   -   a) Symbol contrast, which is “the difference between the highest        and the lowest reflectance values in the profile—in simple terms        the difference between the dark and light areas (including the        Quiet Zones) as seen by the scanner.” (from page 32 of        above-referred GS1 DataMatrix Guideline)    -   b) Print growth (size of the cells in the reconstructed machine        readable code), which “is not a graded parameter but is a very        informative measure for the purposes of process control. It is a        measure of how symbols may have grown or shrunk from target        size. If the growth or shrinkage is too large, then scanning        performance will be impacted.” (from page 34 of above-referred        GS1 DataMatrix Guideline)    -   c) Axial non-uniformity, which “measures and grades (on the 4 to        0 scale) the spacing of the mapping centres and tests for uneven        scaling of the symbol along the X or Y axis” (from page 32 of        above-referred GS1 DataMatrix Guideline); and    -   d) Modulation, which “is related to Symbol Contrast in the sense        that it measures the consistency of the reflectance of dark to        light areas throughout the symbol” (from page 32 of        above-referred GS1 DataMatrix Guideline).

In one embodiment, a voting approach taking into account several ofthese metrics with different weight is used to generate the authenticitymeasure. This enhances the robustness.

In one embodiment, hereinafter referred to as “embodiment E2” (asillustrated by FIG. 15), a patch, logo, and/or marking, the exact shapeof which is known in advance, is printed on object 10. After imagings300 the dispersed electromagnetic radiation (hereinafter referred to asthe “first order image”), a measure of authenticity is generated s400 bydeconvolving s410 the first order image by the expected genuine inkresponse (reference spectrum) and thus computing (reconstructing) asynthetic zero-order image. The reconstructed zero-order image is thenassessed s420 by applying standard image processing quality metrics suchas at least one of: sharpness, intensity of the first derivative,contrast, and dynamic range.

In one sub-embodiment, these quality metrics may be applied separatelyin the direction collinear with the diffraction, or dispersion,direction and the direction perpendicular to the diffraction, ordispersion, direction. The metrics such as sharpness are typically notaltered by the diffraction, or dispersion, when measured perpendicularto the diffraction, or dispersion, direction. But the metrics may bealtered in the direction collinear to diffraction, or dispersion, for anon-genuine mark. The two metrics in the respective two directions aresimilar when the reference spectrum matches the printed one anddissimilar otherwise. A threshold on the similarity may classify theresult of genuine/non genuine.

In one sub-embodiment, these quality metrics may be applied in thedirection collinear with the diffraction, or dispersion, direction only.A simple threshold on the metrics may suffice to classify the result togenuine or non-genuine.

The confidence level of the result of a pattern matching algorithm usingthe reconstructed synthetic non-dispersed pattern may also be used as ameasure of authenticity.

In one embodiment, hereinafter referred to as “embodiment E3” (notillustrated in the drawings), a small dot is printed on object 10 usingan ink that has several distinct spectral peaks. After imaging s300 thedispersed electromagnetic radiation (hereinafter referred to as the“first order image”), a measure of authenticity is generated s400 bydeconvolving s410 the first order image by the expected genuine inkresponse (reference spectrum) and thus computing (reconstructing) asynthetic zero-order image. If the reconstructed synthetic zero-orderimage results in a single dot, the printed ink spectrum matches thereference spectrum and the marking is considered authentic. The analysisof the intensity profile of the reconstructed dot may also providemetrics to determine if the marking is genuine or not.

In one embodiment, hereinafter referred to as “embodiment E4” (notillustrated in the drawings), the marking on object 10 is a solid print,i.e. a uniform deposition of ink without any pattern or modulation ofthickness. A transition between an area containing the printed ink andan area not printed is advantageous to generate some variation in thefirst-order image to allow processing the intensity profile bydeconvolution. The end of the nose of the imaging system may be incontact with the marking and may be equipped with a physical mask withholes, such has, for example: one big square hole, one rectangular hole,a star shaped hole, a grid of several holes of any shape. The mask mayalso be the edge of the nose end itself. The purpose of the mask is tocreate the missing modulation/transition in the printed mark. For theoptical system, there is no difference if a lack of signal is due to anarea without ink, or an area with ink but masked. After imaging s300 thedispersed electromagnetic radiation (hereinafter referred to as the“first order image”), a measure of authenticity is generated s400 bydeconvolving s410 the first order image by the expected genuine inkresponse (reference spectrum) and thus computing (reconstructing) asynthetic zero-order image. The reconstructed zero-order image is thenassessed s420 by applying image processing quality metrics such as thosementioned above in relation to embodiment E2.

The deconvolution step s420 is translation invariant with respect to thespectrum and the position of the first-order image on the sensor. Thismeans that only the shape of the reference spectrum matters. The sameshape but shifted at longer or shorter wavelength would produce the samecomputed zero-order image, but shifted. Therefore, there is typically noway to isolate the shift due the wavelength from a physical shift of themarking position under the imaging system. Embodiments E1, E2 and E3typically suffer from this limitation. Embodiment E4 does not, however,since the modulation is not due to a modulated printing, but due to themask, which position is fixed with respect to the optical system.Indeed, in embodiment E4, there is no way to shift the mask, thus no wayto induce a physical shift of the position of the modulation under theimaging system. Therefore, the absolute position of the reconstructed,synthetic zero-order within the reconstructed image is only related tothe absolute wavelength of the reference spectrum. This absoluteposition is an additional authentication element.

In one embodiment, the deconvolution operation of step s410 is performedper line of the image along the diffraction or dispersion direction.Furthermore, when deconvolution step s410 is carried out on aline-by-line manner, the result of the deconvolution may be thenaveraged to reduce noise and cancel possible modulation by thebackground non-uniformities, prior to comparing the result against thereference spectral information as part of step s420.

In one embodiment, the marking comprises at least one machine readablecode, which may for example comprise at least one of a linear barcodeand a matrix barcode (e.g., a printed Data Matrix code or QR code).

In one embodiment, the marking comprises single spectral characteristicsat least over one region of the marking. The marking may also comprisesingle spectral characteristics over the whole marking.

In one embodiment, a mask is intentionally provided, as part of imagingsystem 200 and in addition thereto, on object 10 or in the vicinitythereof to reveal only a portion of object 10. This is advantageous inthe case the whole object carries a substance having the referencespectral information or a large marking which covers the whole image.The mask artificially creates a transition from non-marked to markedarea even if there would be no such transition without the mask.

FIGS. 18 to 21 provide further explanations regarding some embodimentsof the invention, in particular regarding the advantages of using amask.

On the left-hand side of FIG. 18, two markings, i.e. markings A and B,are shown. They have the same shape but they are not located at the sameposition within the field of view of the system. The same ink has beenused to print markings A and B. On the right-hand side of FIG. 18, therespective images on image sensor arrangement 60 after dispersion areshown. Both images sensed by image sensor arrangement 60 give the sameshape but at different position. Therefore, the position within theimage cannot be used as an authentication factor.

On the left-hand side of FIG. 19, two markings, i.e. markings A and B,are shown. They have the same shape, and are not located at the sameposition within the field of view of the system. Different inks havebeen used to print markings A and B, and they have a spectrum of adifferent shape. On the right-hand side of FIG. 19, the respectiveimages on image sensor arrangement 60 after dispersion are shown. Theimages sensed by image sensor arrangement 60 differ in their shape.Thus, it is possible to discriminate between the two inks, and this canbe used as an authentication factor.

On the left-hand side of FIG. 20, two markings, i.e. markings A and B,are shown. They have the same shape, and are not located at the sameposition within the field of view of the system. Different inks havebeen used to print markings A and B, and they have a spectrum having thesame shape but not at the same wavelength. On the right-hand side ofFIG. 20, the respective images on image sensor arrangement 60 afterdispersion are shown. Both images sensed by image sensor arrangement 60give the same shape at the same position. Therefore, this cannot be usedas an authentication factor.

On the left-hand side of FIG. 21, two markings, i.e. markings A and B,are shown. They have the same shape that is defined by the mask, and theposition within the field of view is defined by the mask. Different inkshave been used to print markings A and B, and they have a spectrumhaving the same shape but not at the same wavelength. On the right-handside of FIG. 21, the respective images on image sensor arrangement 60after dispersion are shown. The images sensed by image sensorarrangement 60 have the same shape but at different position. Thus, itis possible to discriminate between the two inks based on the positionwithin the image (because the only way to move the position is to use adifferent spectrum), and this can be used as an authentication factor.

In one embodiment, imaging system 200 does not use any slit betweendispersive imaging arrangement 30 and object 10. Not using a slit isadvantageous in that this enables acquisition of the dispersed image,without notably having to scan (by moving the imaging device orspectrometer) the surface of the object.

Now, before describing further embodiments of the invention, it may beuseful to discuss some of the advantages brought about by someembodiments thereof, especially compared to prior art systems.

The above-described systems and methods in accordance with someembodiments of the invention are advantageous because they allow theconstruction of simple, compact, snapshot-based (non-scanning), low-costand versatile devices, which may for example be incorporated inhand-held audit devices. Acquiring an image of the dispersedelectromagnetic radiation indeed suffices, together with the referencespectral information which is known in advance and some informationabout the radiation before dispersion (i.e. information about mark 11 onobject 10), to generate the measure of authenticity.

In contrast, imaging spectrometers used for scientific observations, asmentioned above, are typically complex, expensive or bulky. This isbecause these prior art systems usually aim at obtaining high-resolutionspatial and spectral information about all regions of the object orscene.

Mechanical scanning of different bandpass filters in front of an imagerallows reconstruction of a spectral irradiance map of the object I(x, y,λ). However, the time to scan all filters and the complexity andfragility of the scanning mechanism makes the optical system cumbersome,not rugged and costly to implement.

Tuning systems based on Fabry-Perot interferometer or multistage liquidcrystals avoid mechanical complexity but require high-quality and costlyoptical components (i.e. interferometric mirrors). The scanning of thefilter parameters needed to acquire full set of images can be slow andcan become another limitation for the use in handheld authenticationsystems.

Snapshot solutions relying on simultaneous imaging of an object througharray of bandpass filters can achieve fast data acquisition and areespecially adapted to handheld audit devices. Furthermore, such systemsare compact and fit easily in a small volume of a hand-held device. Thelimited number of different passband filters is, however, a drawback,and it is also difficult to obtain suitable lenslet arrays. In addition,the spectral bands of the filter array have to be optimized to the inkspectral response, which prevents the use of off-the-shelf filter arrayswhile custom filter arrays are typically expensive to design andmanufacture.

The example of a grating-based imager using computer tomography (i.e.CTIS) requires either a complex holographically recorded Kinoform typegrating or several crossed gratings able to disperse the light in set oforders around the zero order. The need of several gratings complicatesthe setup and furthermore, the exposure time should be extended tocompensate low efficiency in higher diffraction orders. The dataacquisition is therefore slowed, rendering the setup unsuitable for ahand-held device. Such arrangements also require expensive large sensorswith multi mega-pixels and extensive calculation for the tomographyinversion.

The coded aperture imagers are as slow as the CTIS devices. Moreover,there is an intrinsic problem to reconstruct the full spectrum forspecific design of the coded aperture. Meanwhile, integral fieldspectrometers require cumbersome image slicing optics and requirerelatively large surface image sensors.

Imaging Fourier transform spectrometers are complex instruments relyingon expensive interferometers or birefringent prisms. In either case, thespectrometers require scanning of either an air gap or an angularorientation of the elements to obtain spectra that makes them slow andfragile.

The above-described prior art setups require complex optics and datatreatment algorithms to calculate a full spectral data cube I(x, y, Δ),which is actually not required for authentication purposes. Theinventors have found none of these prior art setups suitable for aneconomical, compact, robust, and fast auditing device based on aspectral imager.

Let us now describe further embodiments of the invention, which may helpunderstand some aspects and advantages of the invention.

In one embodiment, imaging system 200 has an optical setup with atransmission diffraction grating 31 mounted in front of a lens objective32 in a dispersive imaging arrangement 30 which is then arranged infront of image sensor arrangement 60, as schematically illustrated onthe left-hand side of both FIGS. 22a and 22b . System 200 uses a lensobjective 32 or model EO57907 from Edmund Optics Ltd (based in York, UK)with f/2.5 and f=3.6 mm focal length. The dispersive element inarrangement 30 is a transmission diffraction grating 31 of type GT13-06Vfrom Thorlabs, Inc., as mentioned above, with 600 lines-per-mm and 28.7°blaze angle. Area 12 of object 10 is within the field of view of imagingsystem 200.

FIG. 22a also shows, on the right-hand side of the drawing, thesimulated dispersion of a single dot (of, for example, a two-dimensionalmatrix barcode) at three discrete wavelengths obtained by means oftransmission diffraction grating 31 installed in front of imagingobjective 32. The dispersion of the diffraction grating 31 obtained froma Zemax OpticStudio™ simulation is shown. One can see the direct (“Order0”) (not necessarily used in embodiments of the invention) and dispersedimages in first positive (“Order 1”) and first negative (“Order −1”)orders of the single dot (with diameter of 0.5 mm) onto the image spacefor three discrete wavelengths.

More complex marks such as full two-dimensional matrix barcodestypically produce smeared images in the first order of the grating 31due to the specific, broader emission spectra of the inks, and anassociated overlap of the successive spread dots in the direction ofdiffraction is observed, as illustrated on the right-hand side of FIG.22b . In particular, FIG. 22b shows the simulated dispersion of a datamatrix with the non-dispersed image (“Order 0”) (not necessarily used inembodiments of the invention) and two images associated with bothdispersed orders, i.e. the first positive order (“Order 1”) and thefirst negative order (“Order −1”). The direct image in the zero order ofthe grating is not influenced by the grating (except for intensityattenuation) and can be used to decode a printed two-dimensional matrixbarcode. The scale shown on FIG. 22b is in intensity in arbitrary units(“I, a.u.”).

FIGS. 23 and 24 schematically illustrate three imaging systems 200 inthree embodiments of the invention, respectively, showing possiblecomponents of dispersive imaging arrangement 30, such as a transmissiongrating 31, an imaging lens 32, and an optical long-pass filter 33. Area12 of item 10 can be imaged by arrangement 30, considering its field ofview (FOV) 15. Dispersed image 51 of area 12 corresponding to shortestwavelength is indicated. Reference 61 is the window 61 of the imagesensor(s) 63.

Arrangement 30 of FIG. 23 comprises an imaging lens 32, a transmissiongrating 31 (600 l/mm) mounted in front of lens 32 (lens objective EdmundOptics 57907), and an optical long-pass filter 33 mounted behind lens32. As already explained with reference to FIG. 4, this enables toproduce low optical aberrations by using the broad field-of-view of thelens objective.

Grating 31, which is mounted in front of imaging lens 32, deflects thebeams for the first-order and imaging lens 32 receives the input beams.In such a configuration, a wide-FOV imaging lens 32 is used which allowsincident beams at angles specific for the first order.

In arrangement 30 of FIG. 24, both transmission grating 31 (360 l/mm)and optical long-pass filter 33 are mounted behind lens 32 (lensobjective Edmund Optics 57907). As already explained with reference toFIG. 5, this enables to cancel the dependence on the object positionalong the optical axis.

Let us now describe further embodiments of the invention involvingimaging over a plurality of illumination periods, first with referenceto FIGS. 25 and 27 and then with reference to FIGS. 26 and 28. Thesefurther embodiments may naturally be combined with any of theabove-described embodiments.

FIG. 25 schematically illustrates the generation of a measure ofauthenticity of object 10 in one embodiment of imaging system 200. Inthis embodiment, as a first step, image sensor arrangement 60 images theabove-described dispersed electromagnetic radiation 50 in a plurality ofillumination periods t₁, t₂, . . . , t_(n). In one embodiment, n equals2. In another embodiment, n equals 3. Object 10 is illuminateddifferently during each illumination period. Each illumination periodencompasses one imaging period, as schematically illustrated withreference to FIG. 39.

Then, the measure of authenticity is generated. The generation of themeasure of authenticity comprises the following steps.

First, for each illumination period t_(i) (1≤i≤n), an intermediatemeasure of authenticity k_(i) is generated depending at least on arelation between dispersed electromagnetic radiation 50 (A_(i)) imagedat the illumination period t_(i) and a part of the reference spectralinformation, said part of the reference spectral information beingassociated with how object 10 has been illuminated during illuminationperiod t_(i). In one embodiment, intermediate measure of authenticityk_(i) comprises, for each illumination period t_(i), deconvolving thedispersed electromagnetic radiation imaged at illumination period t_(i)by said part of the reference spectral information associated with howobject 10 has been illuminated during illumination period t_(i).

Secondly, the measure of authenticity m is generated based on theplurality of intermediate measures of authenticity k₁, k₂, . . . ,k_(n). This is illustrated on FIG. 25 by the exemplary equation: m=f(k₁,k₂, . . . , k_(n)), wherein f is a function such as for example thearithmetic mean of the intermediate measures of authenticity.

FIG. 27 is a flowchart of an imaging method corresponding to the processillustrated by FIG. 25, wherein the generation s400 of the measure ofauthenticity of object 10 follows image sensor arrangement 60 imagings300 dispersed electromagnetic radiation 50 in a plurality ofillumination periods t₁, t₂, . . . , t_(n). The generation s400 of themeasure of authenticity comprises generating s470, for each illuminationperiod t_(i), an intermediate measure of authenticity k_(i) as describedabove, and then generating s475 the measure of authenticity m based onthe plurality of generated intermediate measures of authenticity k₁, k₂,. . . , k_(n).

In one embodiment, generating s470, for each illumination period t_(i),the intermediate measure of authenticity k_(i) comprises: deconvolving,for each illumination period t_(i), the dispersed electromagneticradiation imaged at illumination period t_(i) by said part of thereference spectral information associated with how object 10 has beenilluminated during illumination period t_(i).

In one embodiment (not illustrated in FIG. 27), the intermediate measurek_(i) of authenticity of each illumination period is generated s470without waiting for the completion of imaging step s300 for allillumination periods. That is, step s470 can be carried out while steps300 is still under way. For example, as soon as image sensorarrangement 60 has imaged dispersed electromagnetic radiation 50 forillumination period t₁, intermediate measure of authenticity k₁ may begenerated s470 for illumination period t₁ and then stored, so thatgenerating step s475 may later be carried out based on all storedintermediate measures of authenticity k₁, . . . , k_(n).

FIG. 26 schematically illustrates the generation of a measure ofauthenticity of object 10, in another embodiment of the invention. Inthis embodiment, as in the embodiment described with reference to FIGS.25 and 27, image sensor arrangement 60 first images dispersedelectromagnetic radiation 50 in a plurality of illumination periods t₁,t₂, . . . , t_(n). The value n may for example be equal to 2 or 3, andobject 10 is illuminated differently during each illumination period.Again, each illumination period encompasses one imaging period, asschematically illustrated with reference to FIG. 40. The measure ofauthenticity is then generated through the following steps:

The imaged dispersed electromagnetic radiation {A₁, A₂, . . . , A_(n)}is processed based at least on the dispersed electromagnetic radiationA₁ imaged at a first illumination period t₁ among the plurality ofillumination periods t₁, t₂, . . . , t_(n) and the dispersedelectromagnetic radiation A₂ imaged at a second illumination period t₂,to produce the processed imaged dispersed part A_(x). All images A₁, A₂,. . . , A_(n) may also be taken into account to produce the so-calledprocessed imaged dispersed electromagnetic radiation composite imageA_(x). That is, the processed imaged dispersed electromagnetic radiationcomposite image A_(x) may be generated based on the dispersedelectromagnetic radiation images imaged at a first to nth illuminationperiods t₁, t₂, . . . , t_(n).

Then, the measure of authenticity m is generated depending at least on arelation between the processed imaged dispersed electromagneticradiation composite image A_(x) and reference spectral information. Inone embodiment, the generation of the measure of authenticity mcomprises deconvolving the processed imaged dispersed electromagneticradiation composite image A_(x) by reference spectral information.

FIG. 28 is a flowchart of an imaging method in one embodimentcorresponding to the process illustrated by FIG. 26, wherein thegeneration s400 of the measure of authenticity follows image sensorarrangement 60 imaging s300 dispersed electromagnetic radiation 50 in aplurality of illumination periods t₁, t₂, t_(n).

Namely, after imaging s300, by image sensor arrangement 60, dispersedelectromagnetic radiation 50 in a plurality of illumination periods t₁,t₂, . . . , t_(n), the measure of authenticity is generated s400. Steps400 comprises, first, generating s482 the so-called processed imageddispersed electromagnetic radiation composite image A_(x) based at leaston the dispersed electromagnetic radiation A₁, A₂ imaged at a first andsecond illumination period t₁, t₂, and preferably based on all dispersedelectromagnetic radiation images A₁, A₂, . . . , A_(n) imaged atillumination periods t₁, t₂, . . . , t_(n). Then, the measure ofauthenticity m is generated s486 depending at least on a relationbetween processed imaged dispersed electromagnetic radiation compositeimage A_(x) and reference spectral information.

In one embodiment, step s482 may be implemented as follows: First, aweighting factor is calculated based on a statistical processing ofpixel values of the first image data A₁ (i.e., the dispersedelectromagnetic radiation imaged at illumination period t₁) and pixelvalues of the second image data A₂ (i.e., the dispersed electromagneticradiation imaged at illumination period t₂). Then, third image dataA_(x) (i.e., the so-called processed imaged dispersed electromagneticradiation composite image) is generated by calculating a weightedcombination using the pixel values of said first image data A₁, thepixel values of said second image data A₂, and said weighting factor.Such an implementation may be performed to maximize the image contrastbetween a dispersed image of marking (e.g. a barcode) and the dispersedimage of remaining background, as described in PCT application WO2014/187474 A1 by the same applicant. WO 2014/187474 A1 disclosestechniques to enhance the image of a mark or code printed overfluorescing background or other backgrounds. Several images of a mark orcode are acquired under different illumination conditions, and an imagesubtraction algorithm suppresses the background to facilitate theextraction of the printed codes from the images.

This embodiment, which will be described in more detail with referenceto FIGS. 29a to 31, can be regarded as a method to enhance the spectralrecognition and authentication of a mark (such as for example a printedmark) on backgrounds (such as for example complex fluorescingbackgrounds), by using an imager with a dispersive imaging arrangement30 (such as for example a transmission diffraction grating) andbackground subtraction using differential images (as described in WO2014/187474 A1). The background subtraction using differential images,as described in WO 2014/187474 A1, will be hereinafter referred to asthe differential illumination background subtraction (DIBS) feature,technique, or algorithm.

This embodiment addresses in particular the following potentialproblems: The dispersed electromagnetic radiation imaged by means ofdispersive imaging arrangement 30, as discussed above, may overlap withthe zero-image and, for example, the fluorescing background of a can cap(or the like) could pose problems for the authentication process. Oneembodiment of the invention to reduce the effect of overlap is to useoptionally an appropriate mask which hides part of the image of object10 to avoid the overlap between the zero- and first-order images of thecode created by means of arrangement 30 (in embodiments in which boththe zero- and first-order of the code are imaged). Such a mask howeveris physical and may complicate the opto-mechanical design of imagingsystem 200.

The DIBS-based embodiment aims at addressing such problems. It usesimages obtained through arrangement 30 which have an overlap between theorders, and a background subtraction using the DIBS technique isapplied. The DIBS technique reduces the effect of fluorescing background(or the like) on the zero-order images (in embodiments in which both thezero- and first-order of the code are imaged) and corrects thefirst-order images (dispersed electromagnetic radiation 50), thusimproving the spectrum-based generation of the measure of authenticity.This is particularly advantageous when the fluorescing background has anexcitation spectrum which differs from the ink to be authenticated (e.g.matrix code).

An example of images of a sample object 10 with fluorescing backgroundobtained with an imaging system 200 of FIG. 1 is shown in FIG. 29a (animage of soft-drink can cap without using a mask). A region withoverlapping zero- and first-order images of sample object 10 can beobserved in FIG. 29a . This region may be unusable for spectrum-basedauthentication purposes.

Therefore, the image of FIG. 29a has two problems: 1) the backgroundvisible in the zero-order overlaps the first order image, and 2) thebackground emits light which is diffracted in the 1^(st) order and mayinterfere “spectrally” with the spectral information to beauthenticated. The first problem may be addressed by using a physicalmask. The DIBS technique specifically addresses the second problem, bysignificantly reducing the background signal from the image.

FIG. 29b shows an image of the same sample object 10 taken with aphysical mask in one embodiment of the invention. No overlap between theorders is present which renders an efficient spectrum-basedauthentication possible, but the useful field-of-view may be limited.Such a limitation may, under certain circumstances, restrict the user tooperate the device only with specific orientations possibly leading toan increase of authentication time for a sample object 10.

In accordance with the above-mentioned DIBS-based embodiment, no mask isused, but images are acquired in a plurality of illumination periods t₁,t₂, . . . , t_(n) with several different illuminations and then an imagesubtraction is carried out in accordance with the DIBS technique. Thisreduces the influence of a fluorescing background (or the like) on boththe decoding (if used) and spectrum extraction.

For example, the DIBS algorithm may use two first order images acquiredby illuminating object 10 with blue and green light respectively. As anoutput of the algorithm, an image is obtained which is the difference orlinear combination of images taken with blue and green illumination.This image typically has better contrast when it comes to the printedcode compared to the initial images, thus improving the performance ofthe decoding engine (if used). The resulting image improves theauthentication process using the first-order image (i.e., dispersedelectromagnetic radiation 50) created by means of dispersive imagingarrangement 30. This effect may be explained by the different excitationspectra for both the ink used to print the code and the fluorescingbackground of object 10 (e.g. a soft-drink can cap). The ink is betterexcited in blue than in green while the background of the soft-drink cancap has mostly the same excitation for both colours. Subtracting theimages then leads to increase of the code contrast and improvedauthentication capability.

FIG. 30 shows examples of images of a soft-drink can cap acquiredwithout a physical mask but excited in two different illuminationperiods by blue light (right-hand image) and green light (left-handimage), in one embodiment of the invention.

FIG. 31 shows examples of background subtracted images using DIBSalgorithm, using respectively the linear combinations B−0.94*G(right-hand image) and 8.22*(B−0.94*G) (left-hand image), in oneembodiment of the invention. In the linear combination B−0.94*G, B is afirst image excited in a first illumination period by blue light, G is asecond image excited in a second illumination period by green light, and0.94 is the weighting factor. In the linear combination 8.22*(B−0.94*G),the significance of B, G and 0.94 are the same as for the first linearcombination, and 8.22 is a scaling factor. Regarding these linearcombinations, the weighting factor and the scaling factor, see equation(1) in WO 2014/187474 A1, page 8, and the corresponding description.

Thanks to the DIBS algorithm, the treated image is more suitable fordecoding (in embodiments in which both the zero- and first-order of thecode are imaged) and improves the spectrum-based generation of themeasure of authenticity.

Let us now describe further embodiments of the invention applicable toboth the imaging over a single illumination period and the imaging overa plurality of illumination periods. These further embodiments may becombined with any of the above-described embodiments.

In one embodiment, object 10 bears a visible or invisible mark 11 (orsign) printed with a printing ink. Such ink contains coloring and/orluminescing agents, such as dye(s) and/or pigment(s) that are typicallyhard to produce and to reverse-engineer. These optical agents may beclassified into two main classes: 1) optical agents producing specificreflective properties upon controlled illumination, and 2) opticalagents producing luminescence upon controlled illumination.

The expected spectral response of said optical agents, when subject toparticular illumination conditions, is known a priori and constitutesthe reference spectral information.

In the case of reflective properties, the spectral response is calledthe spectral reflectivity, which is the fraction of electromagneticpower reflected per unit of wavelength. For example, FIG. 32 shows thespectral reflectivity of two different color pigments (Microlith® fromBASF AG, based in Ludwigshafen, Germany), as measured with aspectrophotometer in reflectance mode (e.g. model DU-640Spectrophotometer from Beckman Coulter Inc., based in Brea, Calif.,U.S.).

In order for the reflectivity to be determined, a known broadbandillumination source may be used, since the wavelength-dependentreflected electromagnetic radiation 20 (spectral radiance, which ismeasured) depends on the incident spectral composition of theillumination (spectral irradiance). The spectral reflectivity may bedetermined either using a calibrated illumination source (in wavelength)or by comparison with a surface of known spectral reflectivity (such asa reference white surface like Spectralon® from LabSphere, based inNorth Sutton, N.H., U.S.) using a non-calibrated broadband light source.The term “broadband” means that the light source emits at least at allwavelengths in the range of interest. Examples of broadband light sourcespectral distribution are shown for a white LED (e.g., an OSRAM OSLONSSL white LED) in FIG. 33 and tungsten filament lamp (incandescent bulb)in FIG. 34 (Source: Schroeder, D. V., 2003. “Radiant Energy,” onlinechapter for the course, ‘Energy, Entropy, and Everything,’ PhysicsDepartment, Weber State University [accessed May 2016]http://physics.weber.edu/schroeder/eee/chapter6.pdf.).

It can be observed from FIGS. 33 and 34 that the spectrum reflected froma given mark strongly depends on the spectrum of the irradiation source.Therefore, the so-called “reference spectral information” should be thespectral reflectivity (reflectance) of the object or mark. Inembodiments where the reference spectral information is the recordedspectral irradiance, said reference spectral information is thenintrinsically related to the spectral distribution of the irradiationsource, which should preferably be controlled when the referencespectral information is recorded the first time (enrolled) and also whenit is measured to determine the authenticity of object 10.

A second class of optical agents covers luminescent dyes or pigments andhas different requirements in terms of illumination and measurement.

Fluorescent dyes and pigments may be selected for example from perylenes(e.g. Lumogen F Yellow 083, Lumogen F Orange 240, Lumogen F Red 300, allavailable from BASF AG). FIG. 35 (source: WO 2016/042025 A1) shows anexample of excitation and emission spectrum of such a fluorescent dye.In particular, it shows the excitation spectrum 601 and emissionspectrum 602 of a fluorescent dye (Lumogen® F Orange 240 from BASF AG)added in an ink used for printing for example a digital code.Double-headed arrow 603 indicates the wavelength range where theemission spectrum can be used as reference spectral information. It canbe observed from FIG. 35 that the excitation spectrum spans betweenabout 400 and 550 nm and the emission spectrum from about 550 to 700 nm.This requires that the illumination source emits at least in the regionof excitation for the fluorescent dye to be excited, but preferably notin the emission spectral region to avoid interfering with thefluorescence emission to be detected, which is typically several ordersof magnitude weaker than the direct reflection.

This illumination and detection scheme is known in the field ofmeasuring fluorescence and usually comprises a narrow band illuminationsource such as for example a single color LED (a blue one at 450 nm or agreen one at 530 nm may be adapted to excite the Lumogen of FIG. 35) anda long pass optical filter in the detection optical path to cut out anyreflection for the tail of the illumination source in the region ofemission. Optionally, a short pass optical filter may also be arrangedbetween the LED and the object 10 to be authenticated.

FIGS. 35 and 36 show emission and excitation spectra for two exemplaryphosphorescent phosphor pigments: Lumilux® blue SN and Lumilux® greenSN-F2Y from Honeywell International, Inc., based in Morris Plains, N.J.,U.S. The spectroscopic properties shown in FIGS. 35 and 36 were measuredon samples printed with silk-screen inks using a spectrofluorometer(Horiba Jobin Yvon Fluorolog model FLIII-22, from Horiba, based inKyoto, Japan). The approach is the same as for the above-describedfluorescent dyes or pigments. Excitation spectra 501 and 511 andemission spectra 502 and 522 of two phosphorescent pigments are used forprinting marks to be authenticated in the form of patch, logo ordesigns. Black arrow 505 on each of FIGS. 35 and 36 indicates thewavelength peak of a deep blue LED at 410 nm which may be used forexciting the phosphorescent pigments efficiently.

In one embodiment, the reference spectral information is generated priorto operating the system and method of authentication. This may be donethrough a recording and registering of the extracted spectralinformation, in the same or very similar conditions of illumination anddetection (for example using the same device or instrument) as the oneto be used in the field.

In one embodiment, a non-controlled illumination source may be used,provided that its spectral characteristics can be determined, through aspectral measurement and a subsequent correction may be made prior toextracting the measured spectral information from object 10 or mark 11to be authenticated.

FIG. 38 is a schematic diagram of an exemplary implementation of acomputing unit 700 that may be used in embodiments of the invention,such as, but not only, for generating the above-discussed measure ofauthenticity.

As illustrated by FIG. 38, a computing unit 700 may include a bus 705, aprocessing unit 703, a main memory 707, a ROM 708, a storage device 709,an input device 702, an output device 704, and a communication interface706. Bus 705 may include a path that permits communication among thecomponents of computing unit 700.

Processing unit 703 may include a processor, a microprocessor, orprocessing logic that may interpret and execute instructions. Mainmemory 707 may include a RAM or another type of dynamic storage devicethat may store information and instructions for execution by processingunit 703. ROM 708 may include a ROM device or another type of staticstorage device that may store static information and instructions foruse by processing unit 703. Storage device 709 may include a magneticand/or optical recording medium and its corresponding drive.

Input device 702 may include a mechanism that permits an operator toinput information to processing unit 703, such as a keypad, a keyboard,a mouse, a pen, voice recognition and/or biometric mechanisms, etc.Output device 704 may include a mechanism that outputs information tothe operator, including a display, a printer, a speaker, etc.Communication interface 706 may include any transceiver-like mechanismthat enables computing unit 700 to communicate with other devices and/orsystems (such as with a base station, a WLAN access point, etc.). Forexample, communication interface 706 may include mechanisms forcommunicating with another device or system via a network.

Computing unit 700 may perform certain operations or processes describedherein. These operations may be performed in response to processing unit703 executing software instructions contained in a computer-readablemedium, such as main memory 707, ROM 708, and/or storage device 709. Acomputer-readable medium may be defined as a physical or a logicalmemory device. For example, a logical memory device may include memoryspace within a single physical memory device or distributed acrossmultiple physical memory devices. Each of main memory 707, ROM 708 andstorage device 709 may include computer-readable media. The magneticand/or optical recording media (e.g., readable CDs or DVDs) of storagedevice 709 may also include computer-readable media. The softwareinstructions may be read into main memory 707 from anothercomputer-readable medium, such as storage device 709, or from anotherdevice via communication interface 706.

The software instructions contained in main memory 709 may causeprocessing unit 703 to perform operations or processes described herein,such as for example generating the measure of authenticity.Alternatively, hardwired circuitry may be used in place of or incombination with software instructions to implement processes and/oroperations described herein. Thus, implementations described herein arenot limited to any specific combination of hardware and software.

FIG. 39 schematically illustrates an example of imaging period andillumination period, in one embodiment of the invention. This drawinghas been already referred to and elaborated upon throughout the abovedescription.

In one embodiment, imaging system 200 comprises, on the one hand, animaging device comprising image sensor arrangement 60 and, on the otherhand, a piece of equipment, hereinafter referred to as “imagingaccessory”, comprising dispersive imaging arrangement 30.

In this embodiment, the imaging device has a built-in camera (includingassociated lenses) and may be a hand-held device, such as for example atleast one of: a mobile phone, a smartphone, a feature phone, a tabletcomputer, a phablet, a portable media player, a netbook, a gamingdevice, a personal digital assistant, and a portable computer device.The imaging device's built-in camera image sensors act as image sensorarrangement 60 in system 200.

As mentioned above, the imaging accessory comprises dispersive imagingarrangement 30, such as for example a transmission diffraction grating,or any other dispersive element as already discussed above withreference to FIG. 1.

The imaging accessory is attachable, directly or indirectly (for examplevia a connecting piece of equipment), to the imaging device so that theimaging accessory's dispersive imaging arrangement 30 is positionedrelative to the imaging device's image sensor arrangement 60 in such amanner that the imaging device and the imaging accessory form an imagingsystem 200 as described above, operable for imaging an object andgenerating a measure of authenticity of the object. In other words, theimaging accessory may be used for example to transform a smartphone intoa portable imaging and authentication system as described above. Theimaging accessory may for example be fixedly positionable over thesmartphone rear camera. The processing and communications capabilitiesof the smartphone may then be used for implementing a processing unit 70of imaging system 200.

Furthermore, if the imaging device has a light source (such as forexample flash LEDs used in a smartphone), said light source may operateas illumination arrangement 210 to illuminate the object 10 to be imagedand authenticated. A smartphone's light source is typically well adaptedfor reflectivity measurements. Alternatively, illumination arrangement210 may be provided as part of the imaging accessory.

This embodiment is advantageous in that the imaging accessory may be apassive accessory, requiring no additional power, and thus providing anaffordable authentication solution.

FIG. 40 schematically illustrates an imaging system 200 in accordancewith the above-described embodiment comprising, on the one hand, animaging device comprising image sensor arrangement 60, wherein theimaging device is a mobile phone having a camera, and, on the otherhand, an imaging accessory 36 comprising dispersive imaging arrangement30. In this exemplary optical setup, imaging accessory 36 comprises adiffraction grating 31 and long pass filter 33 arranged in front of themobile phone camera 64. The mobile phone camera 64 comprises an imagesensor 60 and a built-in lens 66. Optionally, an additional collimatinglens 35 may be positioned in front of imaging accessory 36.

The invention further relates to the following embodiments:

-   Embodiment (X2). Imaging system (200) of claim 1, wherein the    imaging system (200) is an imaging device.-   Embodiment (X3). Imaging system (200) of claim 1, comprising an    imaging device (100) comprising the image sensor arrangement (60)    and the dispersive imaging arrangement (30), wherein the imaging    device (100) is not configured to generate the measure of    authenticity.-   Embodiment (X4). Imaging system (200) of embodiment (X2) or (X3),    wherein the imaging device is a hand-held device.-   Embodiment (X7). Imaging system (200) according to any one of claims    1 to 3 and embodiments (X2) to (X4), wherein    -   the imaging system (200) is configured for generating the        measure of authenticity after the image sensor arrangement (60)        has, in a plurality of illumination periods (t₁, t₂, . . . ,        t_(n)), imaged the dispersed electromagnetic radiation (50); and    -   generating the measure of authenticity comprises:        -   generating, for each illumination period (t_(i)), an            intermediate measure of authenticity (k_(i)) depending at            least on a relation between the dispersed electromagnetic            radiation (50) imaged at the illumination period (t_(i)) and            a part of the reference spectral information, said part of            the reference spectral information being associated with how            the object (10) has been illuminated during the illumination            period (t_(i)); and        -   generating the measure of authenticity (m) based on the            plurality of generated intermediate measures of authenticity            (k₁, k₂, . . . , k_(n)).-   Embodiment (X8). Imaging system (200) of embodiment (X7), wherein    generating, for each illumination period (t_(i)), the intermediate    measure of authenticity (k_(i)) comprises:    -   deconvolving the dispersed electromagnetic radiation (50) imaged        at the illumination period (t_(i)) by said part of the reference        spectral information associated with how the object (10) has        been illuminated during the illumination period (t_(i)).-   Embodiment (X9). Imaging system (200) according to any one of claims    1 to 3 and embodiments (X2) to (X4), wherein    -   the imaging system (200) is configured for generating the        measure of authenticity after the image sensor arrangement (60)        has, in a plurality of illumination periods (t₁, t₂, . . . ,        t_(n)), imaged the dispersed electromagnetic radiation (50), and    -   generating the measure of authenticity comprises:        -   processing the imaged dispersed electromagnetic radiation            based at least on the dispersed electromagnetic radiation            imaged at a first illumination period (t₁) among the            plurality of illumination periods (t₁, t₂, . . . , t_(n))            and the dispersed electromagnetic radiation imaged at a            second illumination period (t₂) among the plurality of            illumination periods (t₁, t₂, t_(n)), wherein the            illumination conditions during the first illumination period            (t₁) at least partially differ from the illumination            conditions during the second illumination period (t₂); and        -   generating the measure of authenticity (m) depending at            least on a relation between the processed imaged dispersed            electromagnetic radiation (A_(x)), and the reference            spectral information.-   Embodiment (X10). Imaging system (200) of embodiment (X9), wherein    generating the measure of authenticity (m) comprises:    -   deconvolving the processed imaged dispersed electromagnetic        radiation (A_(x)) by the reference spectral information.-   Embodiment (X15). Imaging system (200) of claim 6, wherein the at    least one machine readable code comprises at least one of a linear    barcode and a matrix barcode.-   Embodiment (X16). Imaging system (200) according to any one of    claims 5 and 6 and embodiment (X15), wherein the marking (11)    comprises single spectral characteristics at least over one region    of the marking (11).-   Embodiment (X17). Imaging system (200) of embodiment (X16), wherein    the marking (11) comprises single spectral characteristics over the    whole marking (11).-   Embodiment (X18). Imaging system (200) according to any one of    claims 5 and 6 and embodiments (X15) to (X17), wherein the marking    (11) comprises at least one of: optical agents producing specific    reflective properties upon controlled illumination, and optical    agents producing luminescence upon controlled illumination.-   Embodiment (X19). System (220) comprising an imaging system (200)    according to any one of claims 1 to 6, and embodiments (X2) to (X4),    (X7) to (X10), and (X15) to (X18), and an illumination arrangement    (210) for controlled illumination of the object (10).-   Embodiment (X21). Imaging method of claim 7, wherein the imaging    method is carried out by an imaging device.-   Embodiment (X22). Imaging method of claim 7, wherein the imaging    method is carried out by an imaging system (200) comprising    -   an imaging device (100) comprising the image sensor arrangement        (60) and the dispersive imaging arrangement (30), wherein the        imaging device (100) does not generate (s400) the measure of        authenticity.-   Embodiment (X23). Imaging method of embodiment (X21) or (X22),    wherein the imaging device is a hand-held device.-   Embodiment (X30). Imaging method according to any one of claims 7 to    13 and embodiments (X21) to (X23), wherein the dispersive imaging    arrangement (30) comprises at least one of:    -   a diffractive element,    -   a transmission diffraction grating,    -   a blazed transmission diffraction grating,    -   a volume holographic grating,    -   a grism;    -   a reflective diffraction grating, and    -   a dispersive prism.-   Embodiment (X31). Imaging method according to any one of claims 7 to    13 and embodiments (X21) to (X23) and (X30), wherein a slit is not    used between the dispersive imaging arrangement (30) and the object    (10) to be imaged.-   Embodiment (X33). Imaging method of claim 14, wherein the marking    (11) comprises at least one machine readable code.-   Embodiment (X34). Imaging method of embodiment (X33), wherein the at    least one machine readable code comprises at least one of a linear    barcode and a matrix barcode.-   Embodiment (X35). Imaging method according to any one of claim 14    and embodiments (X33) and (X34), wherein the marking (11) comprises    single spectral characteristics at least over one region of the    marking (11).-   Embodiment (X36). Imaging method of embodiment (X35), wherein the    marking (11) comprises single spectral characteristics over the    whole marking (11).-   Embodiment (X37). Imaging method according to any one of claim 14    and embodiments (X33) to (X36), wherein the marking (11) comprises    at least one of: optical agents producing specific reflective    properties upon controlled illumination, and optical agents    producing luminescence upon controlled illumination.-   Embodiment (X39). Computer program or set of computer programs    comprising computer-executable instructions configured, when    executed a computer or set of computers, to carry out an imaging    method according to any one of claims 7 to 15, and embodiments (X21)    to (X23) and (X30) to (X37).-   Embodiment (X40). Computer program product or set of computer    program products comprising a computer program or set of computer    programs according to embodiment (X39).-   Embodiment (X41). Storage medium storing a computer program or set    of computer programs according to embodiment (X39).

Where the terms “processing unit”, “storage unit”, etc. are usedherewith, no restriction is made regarding how distributed theseelements may be and regarding how gathered elements may be. That is, theconstituent elements of a unit may be distributed in different softwareor hardware components or devices for bringing about the intendedfunction. A plurality of distinct elements may also be gathered forproviding the intended functionalities.

Any one of the above-referred units, such as for example processing unit70, or devices, such as for example imaging device 110, may beimplemented in hardware, software, field-programmable gate array (FPGA),application-specific integrated circuit (ASICs), firmware or the like.

In further embodiments of the invention, any one of the above-mentionedprocessing unit, storage unit, etc. is replaced by processing means,storage means, etc. or processing module, storage module, etc.respectively, for performing the functions of the processing unit,storage unit, etc.

In further embodiments of the invention, any one of the above-describedprocedures, steps or processes may be implemented usingcomputer-executable instructions, for example in the form ofcomputer-executable procedures, methods or the like, in any kind ofcomputer languages, and/or in the form of embedded software on firmware,integrated circuits or the like.

Although the present invention has been described on the basis ofdetailed examples, the detailed examples only serve to provide theskilled person with a better understanding, and are not intended tolimit the scope of the invention. The scope of the invention is muchrather defined by the appended claims.

Abbreviations

ASICs application-specific integrated circuita.u. arbitrary unitsCASSI coded aperture snapshot spectral imagerCCD charge-coupled deviceCMOS complementary metal-oxide-semiconductorCTIS computed tomography imaging spectrometerDIBS differential illumination background subtractionFOV field of viewFPGA field-programmable gate arrayl/mm lines per mmLED light-emitting diodeLTI linear translation-invariantMAFC multi-aperture filtered cameraMIFTS multiple-image Fourier transform spectrometerNIR near-infraredRAM random-access memoryRMS root mean squareROM read-only memorySHIFT snapshot hyperspectral imaging Fourier transform spectrometerSWIR short-wavelength infraredUV ultravioletWLAN wireless local area network

1. An imaging system for generating a measure of authenticity of anobject, the imaging system comprising: an image sensor arrangementhaving one or more image sensors; and a dispersive imaging arrangementhaving one or more optical elements, wherein the dispersive imagingarrangement is so that, when electromagnetic radiation from the objectilluminates the dispersive imaging arrangement, at least part of theelectromagnetic radiation is dispersed; and positioned relative to theimage sensor arrangement in such a manner as to allow the image sensorarrangement to image said dispersed electromagnetic radiation so as toobtain a dispersed image; the imaging system being configured for, afterthe image sensor arrangement has, in at least one imaging period, imagedthe dispersed electromagnetic radiation, generating a measure ofauthenticity of the object depending at least on a relation between theimaged dispersed electromagnetic radiation and reference spectralinformation, wherein a synthetic non-dispersed image computed using theimaged dispersed electromagnetic radiation and the reference spectralinformation is used in the generating of the measure of authenticity ofthe object.
 2. The imaging system of claim 1, wherein generating themeasure of authenticity comprises: deconvolving the imaged dispersedelectromagnetic radiation by the reference spectral information.
 3. Theimaging system of claim 2, wherein generating the measure ofauthenticity further comprises determining at least one of: a measure ofdecodability of an imaged machine-readable code in the result of thedeconvolution; a measure of sharpness of the result of thedeconvolution; a measure of blurriness of the result of thedeconvolution; a measure of the dimension of the result of thedeconvolution; a measure of the area of the result of the deconvolution;a measure of the full width at half maximum of a cross-section of theresult of the deconvolution; and a measure of the similarity of theresult of the deconvolution to a reference pattern.
 4. The imagingsystem according to claim 1, wherein the dispersive imaging arrangementcomprises at least one of: a diffractive element, a transmissiondiffraction grating, a blazed transmission diffraction grating, a volumeholographic grating, a grism; a reflective diffraction grating, and adispersive prism.
 5. The imaging system according to claim 1, forimaging an object bearing a marking.
 6. The imaging system of claim 5,wherein the marking comprises at least one machine readable code.
 7. Animaging method for generating a measure of authenticity of an object,the imaging method making use of: an image sensor arrangement having oneor more image sensors; and a dispersive imaging arrangement having oneor more optical elements, wherein the dispersive imaging arrangement isso that, when electromagnetic radiation illuminates the dispersiveimaging arrangement, at least part of the electromagnetic radiation isdispersed; and positioned relative to the image sensor arrangement insuch a manner as to allow the image sensor arrangement to image saiddispersed electromagnetic radiation so as to obtain a dispersed image;and the imaging method comprising: imaging, by the image sensorarrangement, in at least one imaging period, the dispersedelectromagnetic radiation, and generating a measure of authenticity ofthe object depending at least on a relation between the imaged dispersedelectromagnetic radiation and reference spectral information, wherein asynthetic non-dispersed image computed using the imaged dispersedelectromagnetic radiation and the reference spectral information is usedin the generating of the measure of authenticity of the object.
 8. Theimaging method of claim 7, wherein generating the measure ofauthenticity comprises deconvolving the imaged dispersed electromagneticradiation by the reference spectral information.
 9. The imaging methodof claim 8, wherein generating the measure of authenticity furthercomprises determining at least one of: a measure of decodability of animaged machine-readable code in the result of the deconvolution; ameasure of sharpness of the result of the deconvolution; a measure ofblurriness of the result of the deconvolution; a measure of thedimension of the result of the deconvolution; a measure of the area ofthe result of the deconvolution; a measure of the full width at halfmaximum of a cross-section of the result of the deconvolution; and ameasure of the similarity of the result of the deconvolution to areference pattern.
 10. The imaging method according to claim 7,comprising imaging, by the image sensor arrangement, in a plurality ofillumination periods, the dispersed electromagnetic radiation), whereingenerating the measure of authenticity comprises: generating, for eachillumination period, an intermediate measure of authenticity dependingat least on a relation between the dispersed electromagnetic radiationimaged at the illumination period and a part of the reference spectralinformation, said part of the reference spectral information beingassociated with how the object has been illuminated during theillumination period; and generating the measure of authenticity based onthe plurality of generated intermediate measures of authenticity. 11.The imaging method of claim 10, wherein generating, for eachillumination period, the intermediate measure of authenticity comprises:deconvolving the dispersed electromagnetic radiation imaged at theillumination period by said part of the reference spectral informationassociated with how the object has been illuminated during theillumination period.
 12. The imaging method according to claim 7,comprising imaging, by the image sensor arrangement, in a plurality ofillumination periods, the dispersed electromagnetic radiation, whereingenerating the measure of authenticity comprises: processing the imageddispersed electromagnetic radiation based at least on the dispersedelectromagnetic radiation imaged at a first illumination period amongthe plurality of illumination periods and the dispersed electromagneticradiation imaged at a second illumination period among the plurality ofillumination periods, wherein the illumination conditions during thefirst illumination period at least partially differ from theillumination conditions during the second illumination period; andgenerating the measure of authenticity depending at least on a relationbetween the processed imaged dispersed electromagnetic radiation, andthe reference spectral information.
 13. The imaging method of claim 12,wherein generating the measure of authenticity comprises: deconvolvingthe processed imaged dispersed electromagnetic radiation by thereference spectral information.
 14. The imaging method according toclaim 7, for imaging an object bearing a marking.
 15. The imaging methodaccording to claim 7, further comprising a step of controlledillumination of the object.